Add support for using librepo to download packages

Using a metalink or mirrorlist along with the package paths and
checksums allows them to be reliably downloaded even when mirrors are
not all in sync. It will retry with a new mirror until it succeeds, or
has tried all of the mirrors.

osbuild.spec

@@ -37,6 +37,7 @@ Requires:       tar
 Requires:       util-linux
 Requires:       python3-%{pypi_name} = %{version}-%{release}
 Requires:       (%{name}-selinux if selinux-policy-%{selinuxtype})
+Requires:       python3-librepo
 
 # This is required for `osbuild`, for RHEL-10 and above
 # the stdlib toml package can be used instead